1. Field of the Invention
The present invention relates to an image having a PIP (picture in picture) function. Particularly, the present invention relates to a method for removing background noises during the reception of weak electric field signals, in which the background noises (which are generated when the intensity of the electric field of a television broadcast signal is weak) can be reduced.
2. Description of the Related Art
Generally, an image receiver such as a television receiver or a video cassette tape recorder with a PIP function includes a main picture receiving section and a PIP picture receiving section which receive television broadcast signals.
The television broadcast signals which are received by the main picture receiving section and the PIP picture receiving section are mixed together at a PIP section, and then displayed on a screen of a cathode ray tube.
Specifically, the image of the television broadcast signals which has been received by the main picture receiving section is displayed on the whole screen, whereas the image of the television broadcast signals which has been received by the PIP picture receiving section is displayed in the form of a PIP picture on a part of the main picture.
In an image receiver with a PIP function, if the electric field intensity of the television broadcast signals is weak thereby generating background noise, the conventional method of reducing background noise is effected by adjusting the gains of the television broadcast signals that are received through an antenna.
Specifically, the PIP picture receiving section receives the television broadcast signals which have been gain-adjusted in accordance with the electric field intensity of the television broadcast signals which are received by the main picture receiving section.
FIG. 1 is a signal flow chart showing the conventional method for removing the background noise.
As shown in FIG. 1, at step S1, a determination is made as to the electric field intensity of the television broadcast signals which are received by a main picture receiving section.
If the electric field intensity which is determined at step S1 is strong, then at step S2, an LNA (low noise amplifier) is controlled to amplify the reception signals of an antenna so as to adjust the gain to a low level. On the other hand, if electric field intensity is weak, then at step S3, the gain of the LNA is adjusted to a high level.
When the adjustment of the gain of the LNA is completed, a determination is made at step S4 as to whether the user selects a PIP function. If the PIP function is selected, then at step S5, a PIP picture receiving section is activated, and the PIP function is executed. On the other hand, if the PIP function is not selected at step S4, then the PIP function is released at step S6.
Generally, when television broadcast signals are received, a local oscillator operates to convert the received television broadcast signals to intermediate frequency signals. During operation, however, the local oscillator radiates oscillation signals to the outside in the form of "spurious radiation". This spurious radiation not only affects the image receiver, but also affects other nearby electronic apparatuses.
When the PIP function is selected, both the main picture receiving section and the PIP picture receiving section have to be activated. However, when the PIP function is not selected, it is desirable to not have the PIP picture receiving section activated, so as to prevent the generation of spurious radiation.
Further, when the electric field intensity of the received television broadcast signals is low, the spurious radiation from the PIP picture receiving section affects the television broadcast signals which are received by the main picture receiving section.
In the conventional television receiver with a PIP function, if the user selects the PIP function, then power is supplied to the PIP picture receiving section to activate it regardless of the electric field intensity of the received television broadcast signals so as to execute the PIP function.
Therefore, when the electric field intensity of the television broadcast signals which are received by the main picture receiving section is weak, if the PIP function is selected, video signals that are received by the main picture receiving section are affected by the spurious radiation from the PIP picture receiving section. Consequently, background noises are generated, which results in aggravating the quality of the main picture.